import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

class TreeNode{
    TreeNode left;
    TreeNode right;
    int val;
        }
class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> ret = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> list = new ArrayList<>();
            while(size != 0){
                TreeNode cur = queue.poll();
                list.add(cur.val);
                size--;
                if(cur.left != null){
                    queue.offer(cur.left);
                }
                if(cur.right != null){
                    queue.offer(cur.right);
                }
            }
            ret.add(list);
        }
        return ret;
    }
public class Cheshi1 {
    public static void main(String[] args) {

    }

}
